For the treatment of patient's cancer, malignant tumor or the like, an irradiation region of a particle beam is required to be conformed to the shape of a patient's diseased part in order to irradiate to treat the diseased part with a proper dose of the particle beam. To that end, it is important that the shape of a variable collimator composed of a plurality of leaves is properly set, and in addition, that the distribution of both an irradiation dose in a transverse direction and an irradiation dose in a depth direction is homogenized so as to irradiate the whole diseased part with a homogeneous dose. More particularly, it becomes important to confirm the shape of the variable collimator in order to make the irradiation region of the particle beam conform to the shape of the patient's diseased part during the irradiation procedure.
Incidentally, for example, in the following Patent Document 1 (Japanese Unexamined Patent Publication No. 10-76019), a light source to be actuated during the time when a ray beam is stopped in a step for setting a ray system and an optical element (mirror) extended in a radiation path of the ray beam until outside the range of its irradiation region are provided. Visible light is emitted to the optical element by actuating the light source. The visible light received by the optical element is reflected to pass through a collimator and is irradiated to a patient's body surface; and positioning is performed so that its light irradiation field conforms to a region of a target zone.
Furthermore, in the following Patent Document 2 (Japanese Unexamined Utility Model Publication No. 62-186753), a light source consisting of a lamp, a mirror extended in a radiation path of a ray beam until outside the range of its irradiation region, and a TV camera located near the light source are provided for a simulation using a light irradiation field. Light is emitted to the mirror by actuating the light source. The light received by the mirror is reflected to pass through a variable (movable) collimator and is irradiated to a patient's body surface. The relationship between the light irradiation field and the patient is observed by using the TV camera.
Besides, in the following Patent Document 3 (Japanese Unexamined Patent Publication No. 6-246015), a light source, a mirror A extended in a radiation path of a ray until outside the range of its irradiation region, a mirror B provided between the light source and the mirror A, and a TV camera located near the mirror B are provided for confirmation of an irradiation range using a light irradiation field. Light is emitted to the mirror A by actuating the light source. The light received by the mirror A is reflected to pass through a variable (movable) collimator and is irradiated to a patient's body surface. The relationship between the light irradiation field and the patient is copied from the mirror A to the mirror B, and a state copied to the mirror B is observed by using the TV camera.    Patent Document 1: Japanese Unexamined Patent Publication No. 10-76019    Patent Document 2: Japanese Unexamined Utility Model Publication No. 62-186753    Patent Document 3: Japanese Unexamined Patent Publication No. 6-246015    Patent Document 4: Japanese Examined Patent Publication No. 6-96048